This invention relates to semiconductor light emitting devices and manufacturing methods therefore, and more particularly to packaging and packaging methods for semiconductor light emitting devices.
Semiconductor light emitting devices, such as Light Emitting Diodes (LEDs) or laser diodes, are widely used for many applications. As is well known to those having skill in the art, a semiconductor light emitting device includes one or more semiconductor layers that are configured to emit coherent and/or incoherent light upon energization thereof. It is also known that the semiconductor light emitting device generally is packaged to provide external electrical connections, heat sinking, lenses or waveguides, environmental protection and/or other functions.
For example, it is known to provide a two-piece package for a semiconductor light emitting device, wherein the semiconductor light emitting device is mounted on a substrate that comprises alumina, aluminum nitride and/or other materials, which include electrical traces thereon, to provide external connections for the semiconductor light emitting device. A second substrate, which may comprise silver plated copper, is mounted on the first substrate, for example, using glue, surrounding the semiconductor light emitting device. A lens may be placed on the second substrate over the semiconductor light emitting device. Light emitting diodes with two-piece packages as described above are described in Application Serial No. US 2004/0041222 A1 to Loh, entitled Power Surface Mount Light Emitting Die Package, published Mar. 4, 2004, assigned to the assignee of the present invention, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein.
For known power light emitting device packages, a relatively small heat-slug is typically utilized, which may include a portion of the associated electrical leads or an isolated piece. A molded plastic body typically occupies a major part of the package and wraps around the heat spreading component. A lens may be mounted on top of the plastic body and surrounding an optical cavity, and an epoxy or soft gel encapsulant material may be used to fill the cavity. Such a product may not be surface mount technology (SMT) compatible, as its packaging materials generally cannot withstand solder reflow temperatures. In addition, during use, the soft encapsulant may tend to form bubbles or delaminate from the enclosure walls, which may adversely affect device reliability. It is also known to form the lens using a dispensing method capitalizing on the viscosity of a resin used in forming the lens.
It is also known to use transfer molding of epoxy to encapsulate certain low power LED packages, such as miniature surface mountable devices available from Hewlett Packard Corporation. The epoxy on such devices may provide structural strength to the package as well as encapsulating the devices inside. It is also known to use casting to encapsulate LED devices with epoxy. This process typically can only be applied to an open chamber, where curing may occur with the epoxy contained in a cup and a lead frame may be inserted inside the cup and be casted when the epoxy is cured. During curing, a level of liquid epoxy is generally free to adjust itself as a result of chemical reactions and shrinkage in volume.
In some applications, it is desirable to use a side-mounted light emitting device package or other means of direction emitted light at an angle substantially parallel to an underlying substrate. Such packages may be provided using a lead frame technology, and the lead frame may be appropriately bent to support the electrical connections for a side-mounted device. It may also be desirable to provide a narrow angle of illumination in some applications. For example, lighting for cellular telephone screens or the like may utilize a narrow beam of light directed under the display screen and light may need to be launched into a narrow substrate in some applications.